ADE5166_08 AD [Analog Devices], ADE5166_08 Datasheet - Page 52

• Manufacturer Part Number: ADE5166_08
• Description: Single-Phase Energy Measurement IC with 8052 MCU, RTC, and LCD Driver
• Manufacturer: AD [Analog Devices]

ADE5166/ADE5169
Current Channel RMS Calculation
Each ADE5166/ADE5169 simultaneously calculates the rms values
for the current and voltage channels in different registers. Figure 57
shows the detail of the signal processing chain for the rms calcula-
tion on the current channel. The current channel rms value is
processed from the samples used in the current channel waveform
sampling mode and is stored in an unsigned 24-bit register (I
One LSB of the current channel rms register is equivalent to 1 LSB
of a current channel waveform sample.
The update rate of the current channel rms measurement is
4.096 MHz/5. To minimize noise in the reading of the register, the
I
crossing of the voltage input. This configuration is done by setting
the ZXRMS bit (Bit 2) in the MODE2 register (Address 0x0C).
With the different specified full-scale analog input values, the ADC
produces an output code that is approximately ±0d2,684,354 (see
the Current Channel ADC section). Similarly, the equivalent rms
value of a full-scale ac signal is 0d1,898,124 (0x1CF68C). The cur-
rent rms measurement provided in the ADE5166/ ADE5169 is
rms
register can also be configured to update only with the zero
NOTES:
1. WHEN DIGITAL INTEGRATOR IS ENABLED, FULL-SCALE OUTPUT DATA IS ATTENUATED DEPENDING ON THE SIGNAL
I
I
PA
PB
FREQUENCY BECAUSE THE INTEGRATOR HAS A –20dB/DECADE FREQUENCY RESPONSE. WHEN DISABLED, THE
OUTPUT IS NOT FURTHER ATTENUATED.
IBGAIN
HPF
HPF
VOLTAGE CHANNEL
Figure 57. Current Channel RMS Signal Processing with PGA1 = 2, 4, 8, or 16
INTEGRATOR*
MODE1[5]
DIGITAL
dt
LPF1
Figure 58. Voltage Channel RMS Signal Processing
VOLTAGE SIGNAL (V(t))
0xD70B
0x28F5
0x0
HPF1
0xD70A3E
0xD487B0
0x2B7850
0x28F5C2
0x000000
0x000000
Rev. 0 | Page 52 of 148
rms
60Hz
| X |
).
24
CURRENT CHANNEL
WAVEFORM
DATA RANGE WITH
INTEGRATOR ON (60Hz)
CURRENT CHANNEL
WAVEFORM
DATA RANGE WITH
INTEGRATOR OFF
LPF3
accurate to within 0.5% for signal inputs between full scale and
full scale/500. The conversion from the register value to amps
must be done externally in the microprocessor using an amps/LSB
constant.
Current Channel RMS Offset Compensation
The ADE5166/ADE5169 incorporate a current channel rms offset
compensation register (IRMSOS). This is a 12-bit signed register
that can be used to remove offset in the current channel rms
calculation. An offset can exist in the rms calculation due to
input noises that are integrated into the dc component of V
One LSB of the current channel rms offset is equivalent to
16,384 LSBs of the square of the current channel rms register.
Assuming that the maximum value from the current channel
rms calculation is 0d1,898,124 with full-scale ac inputs, then
1 LSB of the current channel rms offset represents 0.23% of
measurement error at −60 dB down from full scale.
where I
sgn
2
I
16
VRMSOS[11:0]
rms
LPF3
rms0
sgn
2
15
=
2
is the rms measurement without offset correction.
25
+
I
2
2
8
rms
26
+
IRMSOS[11:0]
2
2
0
27
7
0x28F5C2
2
+
2
+
6
IRMSOS
2
0x00
18
V
2
rmsx
V
17
rmsx
2
(t)
16
[23:0]
24
×
32
,
0x00
768
I
rms
I
rms
(t)
[23:0]
2
(t).
(4)